An excellent sealing property has been required for a gland packing used for sealing the shaft portion of a rotating and reciprocating apparatus such as a pump.
In the rotating and reciprocating apparatus, the contact portion of the shaft and the gland packing slides when the shaft is operated, and the lubricating property of a contact surface has to be maintained. The maintenance of the lubricating property is insufficient with only a lubricating oil or the like which is impregnated into the gland packing. By usually regulating the fastening pressure of the fastening bolt of a stuffing box, therefore, an internal fluid or an injected liquid is caused to properly leak onto the contact surface of the shaft and the gland packing to put the liquid on the contact surface, thereby maintaining the lubricating property.
In consideration of a sealing property, it is preferable that the amount of leakage should be lessened. If the amount of leakage is too small, however, the attaching portion of the gland packing generates heat so that a frictional force is increased rapidly.
In the case in which the frictional force of the gland packing and the shaft is greater than the power of the apparatus, the operation of the shaft is stopped.
In the case in which the power of the apparatus is greater than the frictional force, there occurs a phenomenon in which the gland packing causes an abnormal friction by the frictional force or a viscosity of the lubricating oil impregnated in the gland packing is reduced due to the generation of heat so that a large amount of lubricating oil flows out, resulting in an abnormal increase in the amount of leakage. (In the present invention, these phenomena will be referred to as “seizing”)
Accordingly, there has been required a gland packing for a rotating and reciprocating apparatus hardly causing the seizing in a small amount of leakage and having an excellent sealing property.
For the prior art of the gland packing for a rotating and reciprocating apparatus, there has been known a gland packing obtained by braiding asbestos, a carbon fiber, an inorganic fiber, an organic fiber or the like and using fluororesin particulates, various waxes, a solid lubricant such as graphite or mica, and furthermore, an oil content having a low viscosity as an impregnant (an impregnant material).
In the case in which a gland packing using an oil type lubricating oil, a fluororesin or the like is utilized for a water type fluid seal, there occurs a problem in that a uniform lubricating film is formed on a contact surface with difficulty due to a water repellency and the amount of leakage has to be increased in order to maintain the lubricating property.
Japanese Patent Laid-Open Publication No. 57-103974 has disclosed a gland packing having a coefficient of friction reduced in use for sealing the water type fluid by utilizing, as an impregnant material for a gland packing, a mixture of polyethylene glycol, a polyacrylic resin or the like to be a hydrophilic resin and a fluororesin particulate, a paraffin wax or the like to be a lubrication holding material.
However, these hydrophilic resins are eluted into water. Therefore, there is a problem in that the hydrophilicity of the gland packing is deteriorated by use for a long period of time.
U.S. Pat. No. 4,256,806 specification has disclosed a technique for forming a yarn itself for the gland packing by a mixture of a fluororesin, graphite and a lubricating oil which act as an impregnant and lubricating material without impregnating the yarn constituted by a fiber material such as asbestos with the impregnant material and the lubricating material. The gland packing formed by braiding the yarn is excellent in flexibility and a lubricating property, and heat generated on the contact surface is quickly diffused by the thermal conductivity of the graphite to an outside so that the seizing is caused with difficulty and a very excellent sealing property can be exhibited.
In use, moreover, an improvement is made in such a manner that the graphite can be prevented from easily flowing out.
In the case in which an abrasion is caused, however, there is a possibility that the graphite might flow out. Therefore, there is a problem in that the gland packing is applied, with difficulty, to uses which do not desire a fluid contamination.
The present invention has been made in order to solve the problems described above, and has an object to provide a gland packing for a rotating and reciprocating apparatus which can maintain an excellent sealing property for a long period of time and can prevent an internal fluid from being contaminated even in the case in which it is used for the shaft seal portion of a water type fluid.